Energy absorber for sodium-heated heat exchanger

ABSTRACT

A heat exchanger in which water-carrying tubes are heated by liquid sodium and in which the results of accidental contact between the water and the sodium caused by failure of one or more of the water tubes is minimized. An energy absorbing chamber contains a compressable gas and is connected to the body of flowing sodium by a channel so that, in the event of a sodiumwater reaction, products of the reaction will partially fill the energy absorbing chamber to attenuate the rise in pressure within the heat exchanger.

United States Patent 11 1 1111 3,924,675

Essebaggers Dec. 9, 1975 [5 ENERGY ABSORBER FOR 3,398,789 8/1968 Wolowodiuk et al 165/134 SODIUNLHEATED HEAT EXCHANGER 3,438,431 4/1969 Dreyer et a] 176/38 X 3,583,479 6/1971 Taylor et a1. 165/134 Inventor: J gg Sueeasanna, 3,748,227 7/1973 Hillekum et a]. 176/38 [73] Assignee: The United States of America as represented by the United States Primary Examiner--Albert W. Davls, Jr. Energy Research and Development Assistant Examiner-S. J. Richter Administration, Washington, DC. 22 Filed: May 3, 1973 [57] ABSTRACT A heat exchanger in which water-carrying tubes are heated by liquid sodium and in which the results of accidental contact between the water and the sodium [52] US. Cl. 165/134; 122/32; 165/40; caused y failure of one or more of th Water tubes is 211 App]. NO.Z 356,879

165/70; 165/ 157; 176/38 minimized. An energy absorbing chamber contains a [51] Int. Cl F28f 9/00 pr l g n i onne ted to the bo y of [58] Field of Search 165/134; 176/38 flowing i m y a hannel so th t, in the event of a sodium-water reaction, products of the reaction will References Cited partially fill the energy absorbing chamber to attenu- UNITED STATES PATENTS ate the rise in pressure within the heat exchanger. 2,971,746 2/1961 Bell 165/134 X 4 Claims, 3 Drawing Figures US. atent Dec. 9, 1975 392,675

' I 5 if ENERGY ABSORBER FOR SODIUM-HEATED HEAT EXCHANGER This invention was made in the course of or under a contract with the United States Atomic Energy Commission.

BACKGROUND OF THE INVENTION One of the more common features found in nuclear power plant designs is the use of liquid sodium to cool the reactor andto transfer heat to water for the generation of steam. The sodium can also be used to transfer heat to steam to thereby superheat the steam. In such designs, superheaters and steam generators must be steam may fail and any contact between the water or steam and sodium can result in a rise in pressure which can cause considerable damage to the heat exchanger. If no provision is made to minimize the effects of such a reaction, the failure of adjacent heat transfer surfaces may follow and therefore, further contact between the reactants may occur. In effect, a chain of water-sodium reactions takes place.

In the case of a sodium-heated steam generator in which water is heated by flowing it through tubes which extendthrough a stream of flowing liquid sodium, the tube failure will result in a violent reaction which may rupture adjacent tubes to cause further contact between sodium and water and an even greater rise in pressure.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome drawbacks found in the prior art such as those discussed above. Accordingly, a sodium-heated steam generator or superheater, with a heat section comprising a number of heated tubes carrying water which is generated into steam, or steam which is super-heated, by a stream of liquid sodium flowing over the tubes, is provided with an energy absorbing chamber, and a channel opening into said chamber and extending into said stream of sodium so that in the event that one or more of said heated tubes should fail, the pressure rise brought about by the consequent sodium-water reaction will be attenuated because a portion of the product of reaction and the sodium will enter said chamber through said channel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a elevational view, partly in section, of a steam generator with an energy absorbing chamber made in accordance with the present invention;

FIG. 2 is a view, partly in section, showing the energy absorber of FIG. 1 and a portion of its supporting structure; and

FIG. 3 is a view, partly in section, of one of the bayonet tube assemblies shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a heat exchanger indicated generally as 10 having a generally cylindrical outer shell 12 with a closed lower end 14. The outer shell 12 includes a sodium inlet 16 and a sodium outlet 18, which is positioned centrally in the closed lower end 14 of the outer heated enters at the water inlet 20 which is located centrally in a dome like upper cover 22. The cover 22 has at its periphery an annular horizontally extending flange 24. The flange 24 and the top of the cylindrical ,shell 12 clamp between them an annular radially extending lip 26 of an upper tube sheet 28.

The upper tube sheet 28 which is generally flat, includes a generally horizontal circular flat portion 29 which is connected to the lip 26 by an annular vertically extending cylindrical sidewall portion 30. The cover 22 and the tube sheet 28 define an enclosed space 32.

Extending through the upper tube sheet 28 and secured to it are a plurality of inner tubes 34, each of which is a component of one of an equal number of bayonet tube assemblies 36. Each of the bayonet tube assemblies 36 has, in addition to its inner tube, an outer tube 38, each of which extends down from a main tube sheet 40. The main tube sheet 40 is below the upper tube sheet 28 and the two tube sheets define along with the cylindrical shell 12, an enclosed space 42.

Each of the outer tubes 38 is closed at its lower end 44, but the inner tubes 34 are open at both ends. Each inner tubes bottom is a little higher than the corresponding closed end 44 of its associated outer tube so that water, either in its liquid phase or its gaseous phase (steam) coming in the inlet 20 and through the chamber 32 will flow downward through the inner tubes 34 to impinge against the closed lower ends of the outer tubes 38 to reverse direction and flow upwardly in the annular spaces between the inner tubes 34 and the outer tubes 38. It is during this upward travel that the water is heated. Thus, the portion of the heat exchanger 10 below the tube sheet 40 is the heat section and the outer tubes 38 are the heated tubes. In a steam generator, liquid water is heated and converted to steam. In a superheater, gaseous water (steam) is heated still further. In either case, steam will collect in the enclosed space 42 and leave the heat exchanger 10 through a steam outlet 46 in the side of the heat exchanger 10 between the upper tube sheet 28 and the lower tube sheet 40.

It has already been explained how a failure of a heat exchanger surface can result in a sodium-water reaction which can cause considerable damage. In order to eliminate, or at least minimize that damage, the heat exchanger 10 is provided with an energy absorber 50. The energy absorber 50 comprises a cylinder 52 closed at its upper end 54. It is supported by six arms 56 which extend from the cylinder 52 to the'inner surface of the outer shell 12. The cylinder 52 with its closed end 54 forms a sidewall which defines an energy absorbing chamber 58. A channel 60 is defined by the open lower end portion of the cylinder 52. A one-way valve 62 is positioned in the channel to allow flow only in an upward direction. Liquid sodium is maintained at a level 64 by gas 66 within the chamber 58.

In the event of a failure of one or more of the outer tubes 38, water or steam within the tube will react with the ambient sodium. The result is an arbupt rise in pressure within the heat exchanger 10. The valve 62 will allow sodium and/or the products of a sodiumwater reaction to pass upward and into the chamber 58 against the pressure of the contained gas 66. The valve 62 will not allow the contents of the chamber 58 to pass downward.

The action of the energy absorber 50 is to absorb a considerable portion of the products of a sodium-water reaction, as well as some of the sodium within the heat exchanger 10. This will attenuate to a considerable degree the pressure rise and pressure oscillation concomtant with the sodium water reaction. Consequently, damage from the reaction will be minimized.

As soon as a sodium-water reaction is detected, remedial steps can be taken. For example, the supply of liquid sodium or water or both can be discontinued. When the pressure is reduced to a safe level, the valve 62 can be opened to allow the contents of the chamber 58 to escape slowly and to eventually flow out of the heat exchanger through the sodium outlet 18.

The foregoing describes but one preferred embodiment of the present invention. Other embodiments are possible without exceeding its scope as defined in the following claims.

What is claimed is:

1. A heat exchanger comprising: an outer shell;

a liquid sodium outlet in said shell;

a liquid sodium inlet in said shell;

a plurality of tubes for carrying water, and extending within said shell between said liquid sodium inlet and said liquid sodium outlet;

an energy absorber wholly within said outer shell having a sidewall defining chamber, a channel opening into said chamber, and a one-way valve, said valve being positioned so that nothing can flow through said channel without flowing through said valve and said valve being operable so that it permits flow only into said chamber until the pressure is reduced to a safe level so that said valve can be opened to allow the contents of said chamber to escape slowly and to eventually flow out of said liquid sodium outlet, said energy absorber being capable of withstanding the pressure resulting from an inadvertant water-sodium reaction over the entirety of said sidewall;

whereby when water is carried by said tubes, said tubes are heated by a stream of liquid sodium flowing from said liquid sodium inlet to-said liquid sodium outlet and said channel extends into said stream of flowing sodium and said chamber con tains gas, an inadvertant sodium-water reaction will result in a pressure buildup which is attenuated because sodium and the products of said reaction will enter said chamber through said channel to compress said gas with the products of said reaction being retained within said energy absorber.

2. The heat exchanger defined in claim 1 wherein said valve is positioned within said channel.

3. The heat exchanger defined in claim 1 wherein said energy absorber comprises a cylinder closed at one end, said channel being positioned at the other end.

4. The heat exchanger defined in claim 3 wherein said cylinder extends generally vertically with the channel being at the lower end thereof. l= 

1. A HEAT EXCHANGER COMPRISING: AN OUTER SHELL; A LIQUID SODIUM OUTLET IN SAID SHELL; A LIQUID SODIUM INLET IN SAID SHELL; A PLURALITY OF TUBES FOR CARRYING WATER, AND EXTENDING WITHIN SAID SHELL BETWEEN SAID LIQUID SODIUM INLET AND SAID LIQUID SODIUM OUTLET; AN ENERGY ABSORBER WHOLLY WITHIN SAID OUTER SHELL HAVING A SIDEWALL DEFINING CHAMBER, A CHANNEL OPENING INTO SAID CHAMBER, AND A NONE-WAY VALVE, SAID VALVE BEING POSITIONED SO THAT NOTHING CAN FLOW THROUGH SAID CHANNEL WITHOUT FLOWING THROUGH SAID VALVE AND SAID VALVE BEING OPERABLE SO THAT IT PERMITS FLOW ONLY INTO SAID CHAMBER UNTIL THE PRESSURE IS REDUCED TO A SAFE LEVEL SO THAT SAID VALVE CAN BE OPENED TO ALLOW THE CONTENTS OF SAID CHAMBER TO ESCAPE SLOWLY AND TO EVENTUALLY FLOW OUT OF SAID LIQUID SODIUM OUTLET, SAID ENERGY ABSORBER BEING CAPABLE OF WITHSTANDING THE PRESSURE RESULTING FROM AN INADVERTANT WATER-SODIUM REACTION OVER THE ENTIRETY OF SAID SIDEWALL; WHEREBY WHEN WATER IS CARRIED BY SAID TUBES, SAID TUBES ARE HEATED BY A STREAM OF LIQUID SODIUM FLOWING FROM SAID LIQUID SODIUM INLET TO SAID LIQUID SODIUM OUTLET AND SAID CHANNEL EXTENDS INTO SAID STREAM OF FLOWING SODIUM AND SAID CHAMBER CONTAINS GAS, AN INADVERTANT SODIUM-WATER REACTION WILL RESULT IN A PRESSURE BUILDUP WHICH IS ATTENUATED BECAUSE SODIUM AND THE PRODUCTS OF SAID REACTION WILL ENTER SAID CHAMBER THROUGH SAID CHANNEL TO COMPRESS SAID GAS WITH THE PRODUCTS OF SAID REACTION BEING RETAINED WITHIN SAID ENERGY ABSORBER.
 2. The heat exchanger defined in claim 1 wherein said valve is positioned within said channel.
 3. The heat exchanger defined in claim 1 wherein said energy absorber comprises a cylinder closed at one end, said channel being positioned at the other end.
 4. The heat exchanger defined in claim 3 wherein said cylinder extends generally vertically with the channel being at the lower end thereof. 